Ultimate7e: Adding 2 extra potentiometers

Having upgraded my 7E to 6 switches, the next thing I worked on was to add 2 potentiometers to it. These will show up as AUX4 and AUX5 inside the DeviationTX firmware.

It’s a slightly trickier process than the switch upgrade, as there are no convenient pins on the main board to use. As such, it requires soldering directly to the pins on the processor. This however, like the processor upgrade, can be done safely if you take the necessary precautions to prevent accidentally creating solder bridges on the processor. Here’s how to get it done.

Hardware needed

First off, here is the list of items you’ll want to have on hand to perform this modification.

Soldering iron with a small size conical tip.

Kapton tape.

30AWG or smaller wire to solder to processor pin (I used 36AWG teflon wire from Hobbyking).

Some male and female pin headers (optional but highly recommended).

Two 5K potentiometers.

Some small gauge wire for general wiring.

Hot glue (optional).

Isolate pin

Kapton tape is used to isolate the pin we want to solder to.

The pins on the processor are small and spaced very closely together. In order to prevent solder bridges, it is better to use Kapton tape to cover and protect the pins that we do not want to get solder onto. In the picture above I used 2 small pieces of Kapton tape to cover all close by pins except pin 14 (PA 0). This pin will be used for AUX4.

Position the wire

36AWG wire taped into position.

Pre-tin and cut the tinned portion to size. After that bend it to the shape you need and tape it into position. I decided to position the wire on to the pad extending off the pin as opposed to having it sit on the pin itself. The wire butts up against the pin nearly flush.

Take your time with this to position it exactly. Make sure that when you hands are removed, the wire sits on the pad with out needing extra pressure.

Solder the wire

Wire successfully soldered onto processor pin.

Once you are happy, clean off your solder tip, dip it quickly into some flux, and touch it briefly to the wire tip. The solder on the pre-tinned wire should melt and bond to both the pad and the edge of the pin.

Both pins after wires are soldered onto them.

Once done with the first pin, gently test the solder joint. If it is good, repeat the same process with pin 20 (PA 4).

Route the new wires

Wires routed to a convenient position on the board.

Once both wires are soldered to the pins, check for solder bridges. Clean them up is necessary, then route the wires so that you have easy access to them. In my case, I attached a 2 pin header to the wires and hot glued it to the main board. Left goes to pin 14 (PA 0 – AUX4) and right is pin 20 (PA 4 – AUX5).

Notice that I left lots of slack in the wire while routing and taped it down in multiple positions. This prevents the wire from accidentally getting caught and pulled. In the event that a small accident should occur, the extra slack allows for some pull before the wires pull the pads or pins.

One other thing I did (that may or may not help), was to try to ensure that the wires cross other signal/power traces on the board at 90°. This is something I do for car audio when dealing with analog signals and trying to reduce induced noise.

Wiring to the potentiometers (Front)

Wiring points to female header at top of case.

We only need to route 3 wires from the front of the case to the back of the case where the potentiometers are mounted. The 3 wires needed are 3v3, PA0/AUX4, and PA4/AUX5. I did this by way of having female pin headers hot glued to the top of the case, so that separation would still be relatively easy.

For the 3v3 supply, I tapped it off of the existing potentiometer. It is the red wire nearer to the bottom of the chassis. Make sure to connect this to the center pin of the connector. This will prevent any damages to your processor should you accidentally flip your connector around.

Wiring to the potentiometers (Back)

Wiring points to the potentiometers.

On the back routing is much easier due to the space available. I terminated everything to a 3 pin male header, again with 3v3 in the center. The ground connection on both potentiometers are connected to each other and to the ground pin available at the battery connector at the bottom of the chassis.

The potentiometers are wired such that 3v3 and ground are on pins 1 and 3 respectively for both potentiometers. This ensures that they will increase/decrease for the same direction of rotation. You may want to test this first with your specific potentiometers using a small battery and a multimeter.

Deviation software upgrade

With all that done, we now need to do 2 more things.

The first is to download and install a new DFU file for devo7e-256. Unfortunately this is still in testing, so a Pull Request has not been sent to the main deviationtx repository for inclusion in the Master branch.

It is available for cloning from my Git repository here. You’ll want to clone the “ultimate7e” branch. I’ll also put it up on the deviationtx.com site under the test build section here. Use the regular steps for flashing any new DFU file.

The next thing to do is to edit the hardware.ini file. You’ll want to uncomment and add extra-switches = potx2 in there. Note that the extra-switches option stacks for Ultimate7E. One line is needed for each type of switch (3-way, 2-way and potentiometer).